Caption: Scanning electron micrograph (SEM) of Bifidobacterium sp. Gram-positive anaerobic bacteria. Bifidobacterium sp. are a large group of probiotic bacteria that are present in the mammalian gastrointestinal tract, mouth and vagina. They are responsible for suppressing pathogenic microorganisms and are rarely pathogenic. Infections due to some species of Bifidobacterium include obstetric and gynaecological sepsis, peritonitis, pulmonary infections, urinary tract infections, bacteraemia and endocarditis. Bifidobacterium sp. are used as a form of probiotic that is thought to have health promoting properties for humans. Probiotic bacteria favourably alter the intestine microflora balance, inhibit the growth of harmful bacteria, promote good digestion, boost immune function, and increase resistance to infection. Magnification: x3,000 when shortest axis printed at 25 millimetres.